Process for preparing removable metal sleeves for gravure printing machines

ABSTRACT

A process for preparing removable metal sleeve for gravure printing machines has been carried out in which after treating the lateral surface of the cylinder with a separator product and after associating protective strips in closure of the through holes of the lateral surface of the cylinder, the same is dipped into an electro-copper plating bath for forming a copper removable sleeve and axial removing of the copper sleeve is obtained by means of compressed air forced to form an air cushion between the cooper sleeve and the lateral surface of the cylinder and by means of a separator product used between the same copper sleeve and the cylinder.

FIELD AND BACKGROUND OF THE INVENTION

In gravure printing a cylindrical form is used to print what is desiredand this is done by a photoengraving process during which tiny cells areformed that receive the ink subsequently transferred onto paper.

The surface on which these cells are engraved by variousmethods--traditional, halftone, conversion, electronic etc.,--isgenerally of copper. Said surface is obtained by galvanic deposition onsteel cylinders and, after photoengraving, is given a chromiumprotective process.

For each fresh set of pictures the cylinders are processed byspecialized engravers and are then sent to the user who mounts them ontomachines for gravure printing.

Bearing in mind the considerable size and weight of each cylinder aswell as the great delicacy of the surfaces, already engraved or preparedfor it, there are clearly problems of transport and storage with relatedcosts and capital tied up for the purpose.

To overcome these drawbacks and lower costs, metal cylindrical sleeves,usually nickel, are used, to slide on and off the cylinders.

A coating of copper, like that deposited on traditional cylinders, isdeposited on the surfaces of these sleeves for good engraving results.There are a various methods for assisting the work of removing sleevesfrom these cylinders. The best known comprises having small holes madein the surface of the cylinder to permit creation of a cushion ofcompressed air between the surface of the cylinder and that of thesleeve.

Considering the great difference between the weight of a sleeve, 2-3kg., and that of the cylinder, 100-200 kg., it is clearly advantageousto have a removable sleeve rather than a conventional type of cylinder.Running costs for corrections, balancing, maintenance, staff andtransport are all reduced.

The quality of print is higher, while adjusting movements are avoided aswell as waste of costly materials.

In the present situation of the market, however, requiring a greatervariety of packing materials, which in turn means shorter printing runsand the ever present need to lower costs to increase competitivity, thefact that sleeves still have to be eliminated after use remains aserious loss and has a negative effect on the market.

A process has therefore been devised whereby a copper film is formed onthe nickel sleeve and a separator product interposed between the two sothat the film can easily be slid off when a new engraving is required. Afresh film for a fresh engraving is then deposited by electroplating onthe nickel sleeve.

The separator product generally consists of a silver-based solution orof passivating substances, bichromates or some others. According to apreferred method a copper film and the separator product are applied tothe nickel sleeve followed by formation of the copper film to bephotoengraved.

To detach the copper film from the sleeve, for a fresh photoengravingprocess, use has to be made of mechanical means.

After this a new film is deposited following application of theseparator. This process offers considerable advantages compared withdirect deposition on the cylinder of the film to be photoengraved.

Even so, however, sleeve costs are high because of the high cost ofnickel and because of the time needed to form the different layers: thecopper film, the separator product and the copper film for engraving.

OBJECTS OF THE INVENTION

The invention here described appreciably lowers costs of removablesleeves both as regards materials and the time needed for applying themand therefore offers considerable economic and practical advantages aswill be explained below.

SUMMARY OF THE INVENTION

Subject of the invention is a process for preparation of metal sleevesfor photoengraving, removable from the cylinder on gravure printingmachines.

The removable sleeve is constructed of copper and engraving is donedirectly onto said sleeve.

The copper sleeve is created on a cylinder by its immersion in anelectro-copper plating bath.

Before being put into the plating bath the cylinder is treated with aseparator product to facilitate detachment of the sleeve.

Once engraved the copper sleeve can be used for further engraving bymechanical removal of the engraved layer.

After formation of the copper sleeve, according to one advantageousapplication of the process, the separator product is once again appliedto the base formed by said sleeve and then a copper film is formed inthe electroplating bath on said base.

In this way, in order to make a fresh engraving, the copper film isremoved from the sleeve with or without mechanical means.

By interposing a separator product, a new film can be formed and a freshengraving be made in the electroplating bath.

The separator product is preferably an aqueous solution of silver salts.This solution of silver salts is that given by an exhausted solutionused to fix films in the engraving process on copper sleeves, loadedwith silver salts which have not been darkened by photographicdevelopment and removed during the fixing process.

It is an advantage if the cylinder exhibits a device able to create anair cushion to assist in sliding the sleeve off the cylinder.

The invention offers evident advantages.

Elimination of the nickel base and copper film, replacing said base by acopper sleeve, not only drastically reduces costs of materials but alsoworking times and simplifies operations.

Photoengraving onto an entirely copper sleeve is much quicker andeasier.

If, by interposition of a separator product, a copper film is formed onthe copper base, a further advantage is gained as removal of the copperfilm for each fresh photoengraving process can be done simply andquickly. It will be seen from the foregoing that removable sleeves offera great many advantages compared with directly photoengraved cylindersboth from the point of view of cost and from that of simplifyingoperations.

BRIEF DESCRIPTION OF THE DRAWINGS

Characteristics and purposes of the invention will be made still clearerby the following examples of its execution illustrated bydiagrammatically drawn figures.

FIG. 1 Perspective of a cylinder for creating an air cushion forformation of a copper sleeve.

FIG. 2 The cylinder in FIG. 1 treated with a solution of separatorproduct.

FIG. 3 The wet cylinder in a bath for electro copper plating.

FIG. 4 The cylinder with its copper sleeve after photoengraving.

FIG. 5 The engraved sleeve removed from the cylinder.

FIG. 6 Sleeve with chromium finish, ready for gravure printing.

FIG. 7 The cylinder after receiving a layer of electro-copper plating,given a new treatment with a separator product.

FIG. 8 The cylinder in FIG. 7 put back into the plating bath forformation of a copper film, at the end of that process.

FIG. 9 The cylinder in FIG. 8, taken from the bath, afterphotoengraving.

FIG. 10 The sleeve of the cylinder in FIG. 9, removed and ready forgravure printing.

FIG. 11 The sleeve in FIG. 10 having received a protective chromiumcoating.

FIG. 12 The sleeve at the end of printing when the photoengraved film isbeing removed to permit formation of a new copper film ready forphotoengraving.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the cylinder 10 with pins 11 are small holes 12 on the surface 13,communicating with the inner chamber 15 in which there is a lateralmouth 14 for passage of compressed air to create an air cushion when thecopper sleeve, to be formed round said cylinder, is being taken off. Thecylinder is treated with a solution 20 of separator product as seen inFIG. 2 and, after application of lateral protective strips 21 on theperforated area, is immersed in the liquid 26 in the bath 25 for electrocopper plating.

The copper sleeve 30 having been formed, the cylinder is extracted forthe photoengraving process of objects 31 as seen in FIG. 4.

The engraved sleeve 30 is then removed (FIG. 5), this action beingassisted by presence of the separator product 20 and by the air cushioncreated by compressed air put into the chamber 15, after which thesleeve 30 is given a protective chromium coating 32 (FIG. 6).

The sleeve is then sent away for gravure printing where it will bemounted on the cylinders of the printing machine.

At the end of the printing run the sleeve can be returned to its ownerswho do the photoengraving.

According to its thickness the sleeve can be remelted or the engravedlayer can be removed, the surface smoothed and the sleeve be used againfor further engraving.

Alternatively, the sleeve can be formed on a cylinder 40 by a layer ofcopper 42, with interposition of a separator product.

The cylinder 40 is given a new bath of separator product 43 and oncemore placed in the copper plating bath 25 for formation of a copper film44 to make a sleeve 45 (FIG. 8).

This film is then photoengraved with the desired design 31 (FIG. 9), thesleeve is removed from the cylinder (FIG. 10) and after receiving aprotective chromium coating 46 (FIG. 11), is sent to the printers.

On completion of the printing run the sleeve 45 is returned to theengraver who can engrave a new design, detaching the film 44 usingmechanical means to do so if required, as shown in FIG. 12 where theedges 47, 48 of the film 44 may be seen in the process of removal.

This having been done, and always with interposition of a separatorproduct, a new film can be formed for a fresh engraving.

Normal photoengraving work comprises preparation of the photographicmaterial for engraving by chemical or by electromechanical methods. Forfixing the photographic film, different solutions are used containing,for example, sodium hyposulphite, bisulphite, ammonium thiosulphate.

These solutions remove the unoxidised silver salts from photographicdevelopment. When this solution is exhausted it will contain a highproportion of silver salts and is therefore sold to engravers who use itas a suitable separator product to interpose between the cylinder andthe copper sleeve or between the copper film and the thicker layer ofcopper in the case of sleeves on which that layer and film are used.

What is claimed is:
 1. Process for preparing removable metal sleeves forgravure printing machines comprising the following steps:preparing acylinder (10, 40) having a lateral surface (13); treating the lateralsurface (13) of the cylinder (10) with a separator product (20)comprising an aqueous solution of silver salts, said solution being anexhausted solution previously used as fixer of a photographic film in aphotoengraving process on a different copper sleeve, said exhaustedsolution being charged with unoxidized silver salts from photographicdeveloping process and removed during a fixing operation; dipping saidcylinder (10, 40) in an electro-copper plating bath (25); forming acopper sleeve (30) directly on the lateral surface (13) of the cylinder(10, 40); extracting the cylinder (10, 40) from the electro-copperplating bath; axially removing the copper sleeve (30) from the cylinder(10, 40) by means of the separator product (20) interposed between thecopper sleeve (30) and said lateral surface (13) of the cylinder (10,40); and photoengraving a design (31) directly on said copper sleeve(30).
 2. Process according to claim 1, further comprising, after theforming step, the steps of:treating an external surface of the coppersleeve (30) with the separator product (20); dipping said cylinder (10;40) carrying the removable copper sleeve (30) with the separator product(20) in the electro-copper plating bath (25); forming a copper film (44)upon said copper sleeve (30), the separator product (20) beinginterposed between the copper film (44) and the copper sleeve (30) andbetween the copper sleeve and the cylinder (10; 40).
 3. Processaccording to claim 2, further comprising the step of mechanicallyremoving the copper film (44) from the copper sleeve (30).